As a generalisation (there are exceptions), County Floras tend to describe frequency and abundance of plant taxa in each county in somewhat inconsistent and non-standardised terms. Terms such as local or common, can refer to overall whole vice-county frequency, or to the actual abundance of a plant where it occurs. It is not always clear what is meant. Frequency is a spatial measure, while abundance is a population measure. Anyone who makes use of the National Vegetation Classification (NVC) will be familiar with the way in which that classification clearly separates these two parameters.
BSBI Rare Plant Registers (RPR) include taxa which are 'Rare' or Scarce' within a vice-county. These are frequency measures; 1 - 3 and 4 - 10 'sites' respectively. These categories do not reflect the actual abundance of the listed taxa, just their spatial frequency. The Excel spreadsheet (link below) applies the same spatial frequency approach as employed to delimit vice-county 'Rare' and 'Scarce', but using seven frequency categories, (Rare, Scarce, Near Scarce, Local, Frequent, Common, and Very Common), it categorises all species and hybrids recorded in a vice-county. The spreadsheet uses tetrad frequency data to categorise taxa, but for 'Rare' and 'Scarce' taxa it also makes use of monad and hectad frequency, while for 'Near Scarce' taxa it also uses monad frequency.
The frequency categories 'Rare' and 'Scarce' used here, are consistent with their use in BSBI Rare Plant Registers. The spreadsheet identifies native and archaeophyte species and hybrids which are Rare or Scarce in a vice-county, and hence should be considered for inclusion in a RPR. The outputs also clearly show the number of taxa with no recent records in a vice-county.
EDIT ADDED 20/01/2015
Following further testing of the spreadsheet, a revised version (dated 19th January 2015) is now available. Updated links to the Excel file and Explanatory notes are given in a post below, dated 16/2/2018.
The Explanatory Notes must be read carefully. Please do not be put off by their length and detail, as the Excel analysis file is much easier for you to use, than the notes were for me to write!
However, if new to running DDb queries, and copying, pasting and sorting data in Excel, it may be a little daunting. I think the results are worth it though. Tom H. is going to see if this type of analysis, or something similar, can be made more easily available within the DDb. In the meantime please make use of the version provided at the link above.NB there are some limitations on how the spreadsheet works for vice-counties in Ireland. These are explained in the Explanatory notes.
EDIT ADDED 21/01/2015
The capacity of the spreadsheet has been increased from 2000 to 3250 taxa. This should provide enough capacity for even the most diverse vc, with the most assiduous recording of aliens, critical taxa etc..
Andy.